This invention relates to shape-recovering material, especially in a tubular form, and, more particularly, to shape-recovering material with printed matter thereon.
Shape-recovering material, sometimes also called heat-shrinkable material, is widely used in marking and packaging applications. A working definition used herein is that the shape-recovering material is a polymer having materials properties described by a recovered state and an expanded state which contracts toward the recovered state upon heating. When the shape-recovering material is provided in tube form, it is typically structured to contract to or toward a specified size in the recovered state. In its initial manufacturing, the shape-recovering material is typically extruded in a particular shape and size, expanded to the expanded state, and thereafter cooled so that the expanded state is retained. When it is to be applied in service, the expanded and cooled material is placed overlying a body to be enclosed, and then again heated so that it contracts back toward the recovered state, thereby enclosing the body in a polymeric covering.
In a marking application, a tube of shape-recovering material is extruded, heated and expanded circumferentially by internal pressure, and cooled. At a later time, it is printed with printed matter. The printed tube is placed overlying a length of electrical wire, such as one or more lengths of electrical wire in a wiring harness. The tube is heated, so that the tube shrinks around the wire(s), thereby identifying the enclosed wire(s) by the applied printed matter in a manner that does not interfere with the function and does not require the use of tags or the like.
When the tube is shrunk, the printed matter distorts, because the tube shrinks circumferentially by a substantial amount but very little axially. For example, if the tube is circumferentially shrunk by a contraction ratio of 3:1 in the final contraction onto the wire, the height of any printing on the tube distorts in the circumferential direction by a factor of about 3:1. The printing is often so distorted either before or after shrinking that it may be difficult to read in one state or the other. If the printed matter is applied in a pre-distorted condition that compensates for the distortion that occurs during shrinking, it will be difficult to read prior to shrinking. If the printed matter is applied in the same proportions as desired on the final shrunk tube, the distortion during shrinking makes the printing difficult to read after shrinking. Additionally, there is no certainty that the shape-recovering material will always shrink fully and uniformly to the recovered state, so that the degree of distortion is not predictable.
There is a need for a technique for making and using shape-recovering material with printed matter thereon, where the printed matter does not substantially distort as the shape-recovering material is applied to a body to be enclosed. The present invention fulfills this need, and further provides related advantages.
The present invention provides a shape-recovering material, a method for its production, and a method for its use with or without printed matter thereon. The printed matter, when present, does not distort during the shrinking of the shape-recovering material onto the body to be enclosed. If the shape-recovering material contracts only partially and/or nonuniformly in the final shrinking operation, the printed matter remains readable and substantially undistorted. The present approach may be utilized with only minor changes to the production of the shape-recovering material.
In accordance with the invention, an article comprises a layer having a circumferential direction and a longitudinal reference direction lying in the layer and perpendicular to the circumferential direction. The layer is made of a shape-recovering polymeric material having materials properties described by a recovered state and an expanded state which contracts toward the recovered state upon heating. The layer has a first region in the recovered state, with the first region comprising one or more stripes extending parallel to the longitudinal reference direction. There is also a second region in the expanded state. In a preferred application, there is printed matter on the first region.
In a particularly preferred embodiment, the article is a hollow tube having a direction of elongation and a tube wall. The tube wall is made of a shape-recovering polymeric material having materials properties described by a recovered state and an expanded state which contracts toward the recovered state upon heating. The tube wall has a first region in the recovered state. The first region comprises one or more stripes extending parallel to the direction of elongation, preferably with printed matter on the first region. There is also a second region in the expanded state.
The article may be made of any known or newly discovered type of shape-recovering material having the properties described herein. Examples of such materials include polyolefins, polyvinylidene fluoride, polychloroprene, polyvinyl chloride, polyethylene terephthalate, silicone rubber, polytetrafluoroethylene, fluorinated ethylene propylene, and ethylene-tetrafluoroethylene.
The article is used to enclose a body. In a preferred embodiment, the article is a tube placed overlying an electrical wire, or a bundle of electrical wires, and then shrunk into a snug fit over the wire(s).
A method in accordance with the invention for enclosing a body comprises the steps of providing a piece of shape-recovering material having materials properties described by a recovered state and an expanded state which contracts toward the recovered state upon heating. The piece is processed to have a first region in the recovered state, a second region in the expanded state, and, preferably, printed matter on the first region. The piece is positioned overlying the body, and the second region is heated so that it contracts toward the recovered state, thereby shrinking around the body. The step of processing is preferably accomplished by one of two techniques, with a starting material having the first region in the recovered state and the second region in the recovered state. In one preferred technique, the first region is expanded to the expanded state and the second region is expanded to the expanded state, usually simultaneously, and thereafter the first region is recovered to the recovered state. The printed matter, where used, is thereafter applied to the first region. In the other preferred technique, the second region is expanded to the expanded state while maintaining the first region in the recovered (in this case, unexpanded) state. The printed matter, where used, is thereafter printed onto the first region. The piece of shape-recovering material may be a piece of tube.
The present invention allows high-shrinkage shape-recovering materials to be used in applications which otherwise would not be feasible because of the distortion of printed matter during heat-induced contraction from the expanded state to the recovered state. It is desirable to use printed tubes having a contraction ratio of at least about 4:1 for marking some types of wire bundles to which connectors are already attached, because the expanded tubes can be slipped over the enlarged connectors at the ends of the bundles and then contracted to fit snugly onto the wires of the wire bundle. Conventional tubing usually cannot be used for this application, because the distortion of the printing during the contraction of 4:1 or greater makes the printing unreadable. With the present approach, because there is substantially no distortion of the printing during contraction, printed tubes having a contraction ratio of 4:1 or greater can be used for this and other applications. Printed tubes of shape-recovering materials can therefore be utilized in a wider range of applications than heretofore possible.
In the approach of the invention, the piece of the shape-recovering material is apportioned into two regions, which are processed differently. When it is used in the preferred application, printed matter is applied only to the material in the recovered state, and which does not subsequently shrink during heating. There is therefore substantially no distortion of the printed matter during contraction. Other features and advantages of the present invention will be apparent from the following more detailed description of the preferred embodiment, taken in conjunction with the accompanying drawings, which illustrate, by way of example, the principles of the invention. The scope of the invention is not, however, limited to this preferred embodiment.